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RCMD(3SOCKET)							 RCMD(3SOCKET)

NAME
       rcmd,  rcmd_af, rresvport, rresvport_af, ruserok - routines for return‐
       ing a stream to a remote command

SYNOPSIS
       cc [ flag ... ] file... -lsocket	 -lnsl	[ library... ]
       #include <netdb.h>
       #include <unistd.h>

       int rcmd(char **ahost, unsigned short inport, const char *luser,
	    const char *ruser, const char *cmd, int *fd2p);

       int rcmd_af(char **ahost, unsigned short inport, const char *luser,
	    const char *ruser, const char *cmd, int *fd2p, int af);

       int rresvport(int *port);

       int rresvport_af(int *port, int af);

       int ruserok(const char *rhost, int suser, const char *ruser,
	    const char *luser);

DESCRIPTION
       The rcmd() function is used by the superuser to execute a command on  a
       remote  machine	with  an  authentication scheme based on reserved port
       numbers. An AF_INET socket is returned with rcmd(). The rcmd_af() func‐
       tion supports AF_INET, AF_INET6 or AF_UNSPEC for the address family. An
       application can choose which type of  socket  is	 returned  by  passing
       AF_INET	or  AF_INET6 as the address family. The use of AF_UNSPEC means
       that the caller will accept any address family. Choosing AF_UNSPEC pro‐
       vides a socket that best suits the connectivity to the remote host.

       The  rresvport()	 function  returns  a  descriptor  to a socket with an
       address in the privileged port space. The  rresvport_af()  function  is
       the  equivalent	to  rresvport(), except that you can choose AF_INET or
       AF_INET6 as the socket address family to be returned by rresvport_af().
       AF_UNSPEC does not apply to the rresvport() function.

       The  ruserok()  function	 is  a routine used by servers to authenticate
       clients that request as service with rcmd.

       All of these functions are present in the same file and are used by the
       in.rshd(1M) server among others.

       The rcmd() and rcmd_af() functions look up the host *ahost using getad‐
       drinfo(3SOCKET) and return −1 if the host does  not  exist.  Otherwise,
       *ahost  is  set	to  the	 standard name of the host and a connection is
       established to a server residing at the Internet port inport.

       If the connection succeeds, a socket in the  Internet  domain  of  type
       SOCK_STREAM  is	returned  to  the  caller.  The socket is given to the
       remote command as standard input (file descriptor 0) and standard  out‐
       put (file descriptor 1). If fd2p is non-zero, an auxiliary channel to a
       control process is set up and a descriptor for it is placed  in	*fd2p.
       The  control process returns diagnostic output file (descriptor 2) from
       the command on the auxiliary channel. The control process also  accepts
       bytes  on this channel as signal numbers to be forwarded to the process
       group of the command. If fd2p is 0, the standard error (file descriptor
       2)  of  the  remote command is made the same as its standard output. No
       provision is made for sending arbitrary signals to the remote  process,
       other than possibly sending out-of-band data.

       The protocol is described in detail in in.rshd(1M).

       The  rresvport()	 and  rresvport_af()  functions	 are  used to obtain a
       socket bound to a privileged port number. The socket  is	 suitable  for
       use by rcmd() and rresvport_af() and several other routines. Privileged
       Internet ports are those in the range 1 to 1023. Only the superuser  is
       allowed	to  bind a socket to a privileged port number. The application
       must pass in port, which must be in the range 512 to 1023.  The	system
       first  tries to bind to that port number.  If it fails, the system then
       tries to bind to another unused privileged port, if one is available.

       The ruserok() function takes a remote host name returned by  the	 geth‐
       ostbyaddr() function with two user names and a flag to indicate whether
       the local  user's  name	is  that  of  the  superuser.  See  gethostby‐
       name(3NSL).    The   ruserok()	function   then	  checks   the	 files
       /etc/hosts.equiv and possibly .rhosts in the local user's  home	direc‐
       tory  to	 see  if  the  request	for  service  is allowed. A 0 value is
       returned if the machine name is listed in the /etc/hosts.equiv file, or
       if the host and remote user name are found in the .rhosts file.	Other‐
       wise, the ruserok() function returns −1. If the superuser  flag	is  1,
       the /etc/hosts.equiv is not checked.

       The error code EAGAIN is overloaded to mean "All network ports in use."

RETURN VALUES
       The  rcmd()  and	 rcmd_af()  functions return a valid socket descriptor
       upon success. The functions returns −1 upon error and print a  diagnos‐
       tic message to standard error.

       The  rresvport()	 and  rresvport_af()  functions	 return a valid, bound
       socket descriptor upon success. The functions return −1 upon error with
       the global value errno set according to the reason for failure.

FILES
       /etc/hosts.equiv
			   system trusted hosts and users

       ~/.rhosts
			   user's trusted hosts and users

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌───────────────┬─────────────────┐
       │ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
       ├───────────────┼─────────────────┤
       │MT-Level       │ Unsafe		 │
       └───────────────┴─────────────────┘

       This  interface	is Unsafe in multithreaded applications. Unsafe inter‐
       faces should be called only from the main thread.

SEE ALSO
       rlogin(1),  rsh(1),  in.rexecd(1M),   in.rshd(1M),   Intro(2),	getad‐
       drinfo(3SOCKET), gethostbyname(3NSL), rexec(3SOCKET), attributes(5)

				 Feb 10, 2004			 RCMD(3SOCKET)
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